Research On Intrinsically Safe Methane Detector In Coal Mine

Coal is an important strategic energy with the largest reserves and the most widespread distribution in the world,and it plays an important role in human production and life,such as smelting steel,generating electricity and heating.Underground mining is the main way to obtain coal,and the gas accumulated in the coal rock may cause catastrophic accidents such as explosions,which will pose a serious threat to the lives of the miners.The main component of methane gas is methane,and monitoring the concentration of methane gas can help early warning of gas explosions.According to national regulations,electrical equipment working in such a complex gas environment needs to take protective measures to avoid thermal effects or electric sparks igniting gas.Among many explosion-proof types,the intrinsically safe type limits the energy in the circuit to make it"essentially"safe and reliable.Therefore,it is necessary to study an intrinsically safe methane detector in coal mine.This paper is based on the principle of infrared absorption spectroscopy to detect the concentration of methane gas,and combines Tunable Diode Laser Absorption Spectroscopy（TDLAS）technology with Wavelength Modulation Spectroscopy（WMS）technology to develop an intrinsically safe methane detector in coal mine,of which the intrinsically safe type is the focus of research.Firstly,the technical principle and implementation method of TDLAS-WMS were introduced in detail,and the structure of the detector was designed,including the laser and the gas cell.The design of intrinsically safe circuits were mainly from the control of thermal effects and suppression of electric sparks.According to national standards,the thermal effects were learned by evaluating the maximum surface temperature of chips,wires,and printed lines;the minimum ignition curves were used as a reference for limiting the capacitance and inductance values in the circuit.The intrinsically safe power supply protection module,laser temperature control drive module,digital signal processor module and detector module were designed one by one,and the voltage value,current value and operating temperature were tested after welding and debugging.After that,the software were designed to realize the communication between the human-computer interaction screen and the main controller based on the Modbus protocol.By designing the display interface and writing related programs,the methane gas concentration,laser temperature and current data were displayed on the screen.Finally,the linear relationship between the amplitude of the second harmonic signal and the concentration of methane gas was obtained through the gas calibration experiment.When the average time is 28 s,the lowest detection limit of the detector is 0.08×10^-6（volume fraction）.The innovation of this paper:For the special gas environment in coal mines,the electrical part of the methane detector is designed to be intrinsically safe,the intrinsically safe circuit design process is proposed,and the circuit modules are tested,and an intrinsically safe methane detector in coal mine based on TDLAS-WMS technology is developed.